The present invention relates to electrical connectors useful in many applications, but particularly intended for use in hostile environments. More specifically, the present invention relates to single and multi-pin electrical connectors for use in high-pressure, high-temperature applications which commonly occur in the oilfield, but which are also encountered in geothermal and research applications.
Oil wells are being drilled to deeper depths and encountering harsher conditions than in the past. Many of the electrical connectors in the oilfield are exposed to the environment of the open well bore, where at maximum depth, pressures rise to over 30,000 psig, temperatures exceed 500° F., and the natural or chemically-enhanced well bore environment is extremely corrosive. In part because of these conditions, many downhole tools are oil-filled, but regardless of whether the tools are oil- or air-filled, the high temperatures and pressures of oil wells require the use of specially-designed electrical connectors for both power and communication to such tools. Metal connectors with glass seals such as those described in U.S. Pat. No. 3,793,608 were developed for use in these hostile environments. Such connectors are available from a number of vendors, including Kemlon Products and Development Co., Ltd. (Pearland, Tex.), Hermetic Seal, and Deutch and, up until the last five years or so, have given good service. Another variety of connectors, developed by Kemlon Products in the early 1980's and in the early 1990's by Schlumberger Well Services (Houston, Tex.), and currently manufactured by Kemlon Products and by Greene, Tweed (Houston, Tex.), utilizes a thermoplastic housing constructed of very high temperature housing material such as the aromatic polyether ketones (PEEK, PEK, PAEK, and PEKK) and conductors of various metals. However, as wells have gone deeper and simultaneous temperature and pressure conditions have increased, the environment for these connectors has become increasingly hostile, and certain disadvantages and limitations of both types of connectors have come to light.
Existing connectors can fail in at least two ways. The more common failure mode for glass-sealed connectors is caused by the almost inevitable presence of moisture and by well bore chemicals, either of which can cause current to arc, or short, from the conductor to the metal body of the connector. Because glass-sealed connectors utilize a metal shell to house the glass-sealed pin conductors, the presence of moisture in the vicinity of the pins may cause arcing or electrical leakage between pins or from pins to ground. Although expensive because they require that the electrical apparatus be pulled from the well, most such electrical failures are repairable in that the apparatus can be repaired and the connector replaced.
Conditions are improved in connectors in which ceramic insulation extends the insulating distance, or arc path, but the problem is not solved by the use of such materials. Because they are such a precise assembly of different materials, glass to metal sealed connectors are particularly affected by exposure to a wide range of operating temperatures. The effect results from the different coefficients of thermal expansion between the metal and the glass, which can cause cracking of the glass as temperatures increase over a wide range of operating temperatures, i.e., −100° F. to over 500° F. Such temperature ranges are encountered, for instance, in oilfield operations in the Artic, where a tool with many connectors may be put into service at an ambient surface temperature of −100° F. and then lowered 30,000 feet into a “hot” formation deep in the earth. This differential expansion problem was recognized in the afore-mentioned U.S. Pat. No. 3,793,608, and may result in the electrical failure described above.
To address this problem, the ceramic material used to extend the insulation must be chosen to match the glass in thermal expansion. Otherwise, the thermal cycling could break the bond between the glass and the ceramic, presenting a possible arc path between the pin and body at the ceramic glass interface. Ceramic materials are available with thermal expansion coefficients that match the types of glass utilized in such conductors, and that also have desirable dielectric properties and high compressive strengths, but they have low tensile and flexural strengths. Because space limitations frequently require pin patterns that are closely spaced in the connector and the ceramic material is not strong in flexural strength, the extended ceramic may become cracked internally, for instance, when a pin is bent and then straightened out. The damage to the ceramic is almost impossible to detect visually and with the presence of moisture, frequently leads to arcing, electrical leakage, and direct shorts. Further, the short may be unexpected because the connector, or even the electrical apparatus having the connector installed thereon, tested normally on the surface (at room temperature and in a dry environment), but when the electrical apparatus is run downhole, the short suddenly appears.
Previous attempts to improve the glass-sealed, metal connector have met with varying degrees of success. For instance, ceramic materials are known to have excellent dielectric properties, to be very strong in compression (for instance, from high ambient pressure), and to be highly resistant to acid, alkali, water, and organics, and would therefore seem to present an ideal material for inclusion in such connectors. However, ceramics are brittle, and oilfield personnel are not well known for their careful handling of equipment such that connectors including ceramic materials are prone to the kind of electrical failure described above when a pin is bent, for instance. Further, in the higher temperature environments of the wells currently being drilled, even connectors comprised of ceramic materials suffer from the above-characterized problem of differential thermal expansion and the resulting electrical failure.
Another improved version of the glass-sealed, metal connector utilizes a wafer, or cap, comprised of a very high temperature thermoplastic material having favorable dielectric properties (such as PEEK or PEK) that is bonded, or epoxied, to the metal body of the connector to provide a longer arc path, resulting in increased insulation resistance and a more flexible and “forgiving” insulator that is less prone to damage from bending moments exerted on the pin(s). However, in adverse conditions, a problem that has arisen with some connectors having such a plastic “cap” is that it is possible for water to accumulate under the cap. When water accumulates under the cap of such connectors, the water provides an electrically conductive path between the pins and/or between the pins and the metal body that results in an undesired electrical leakage or a distortion in the electrical signal from the electrical apparatus.
Although the second failure node also occurs in connectors other than those that utilize thermoplastic materials, connectors that utilize thermoplastic materials are widely used in the oilfield, and therefore provide a good illustration of the problem. This second failure mode is referred to as hydraulic leakage and is the more disastrous in that it results in serious and expensive damage to the electrical apparatus and, in the case of an electrical apparatus that is a downhole tool or instrument, expensive and embarrassing lost time on the rig floor because the entire tool must be pulled from the well and rebuilt or replaced. Thermoplastic materials are molded at high temperature and pressure and have the very significant advantage of resisting moisture. Arcing distances are naturally greater for a connector of the same geometrical structure because there is no metal body for the pins to short to. Further, a pin that bends may not cause shorting problems because the thermoplastic is flexible and does not easily break or crack. A further advantage of such connectors is that because the conducting pins are sealed to the plastic during the molding process, the moisture does not leak along the pin inside the connector even when pins have been bent and then straightened.
However, a characteristic of thermoplastic materials is that they can be re-molded if later exposed to conditions of temperature and pressure of the type likely to be encountered, for instance, in deep oil wells. Creep, sometimes referred to as cold-flow, occurs when the conditions of temperature and pressure cause a change in the shape of an item. At the extremes found in oilfield applications, temperatures and pressures approach the molding conditions of these high temperature thermoplastics, and cold-flow becomes significant as the plastic extrudes though the spaces between the pin of the connector and the surrounding metallic oil tool housing or connector support plate. In some cases, the molded pin can move enough to cause an interruption in the electrical signal, and in others the plastic flows enough to cause a hydraulic failure. In this failure mode, either through mishandling or because the connector is subjected to conditions that exceed the capabilities of the materials or the construction of the connector, the integrity of the connector is compromised. As a result of such hydraulic failure, the connector becomes the route for the ingress of steam, water, or other fluid(s) from the well bore and into the electrical apparatus, driven by the high downhole pressure, and hence the electrical apparatus is severely damaged or destroyed.
This list of the disadvantages and limitations of known connectors is not intended to be exhaustive, but is intended instead to illustrate some of the difficulties caused by the construction and the materials utilized in such connectors.
As is apparent from this summary of known and/or presently available connectors for hostile applications, there is a need for, and it is an object of the present invention to provide, a connector that maintains favorable electrical performance properties even when utilized in high-pressure, high-temperature applications.
There is also a need for an electrical connector including thermoplastic materials in which the cold flow of the thermoplastic material is restricted, or even prevented, in high-temperature and/or high-pressure environments to provide a primary seal to the bulkhead of the electrical apparatus to which the connector is engaged, on the high pressure side of the connector ahead of the glass-to-metal seal, brazed ceramic seal, or glass-ceramic seal and forming an internal seal between the conductor and the external environmental fluids, and it is an object of the present invention to provide such an apparatus and method.
Another object of the present invention is to provide an electrical connector that provides a long arc path between the metal body of the connector and the central conductor, and maintains the length of that arc path under high-temperature and/or high-pressure conditions, so as provide favorable electrical performance in hostile applications.
Another object of the present invention is to provide an electrical connector that maintains its favorable electrical properties at temperatures and pressures up to and exceeding 500° F. and 30,000 psi.
Another object of the present invention is to provide an electrical connector that maintains its favorable electrical properties at high temperatures and pressures and that includes structure that provides strain relief from bending moments applied to the conductor(s) of the connector.
Yet another object of the present invention is to provide an electrical connector utilizing thermoplastic materials which are press fit, molded over, or shrink fit onto the conductor and in which, to the extent that any cold flow does occur upon exposure of the thermoplastic material to high-temperature and/or high-pressure conditions, the thermoplastic material fills every void around the conductor to improve the insulation properties of the connector.
Another object of the present invention is to provide an electrical connector that combines the hydraulic advantage of the glass-sealed connector with an overmolding of thermoplastic material such as an aromatic polyether ketone having a structure that resists cold flow, moisture, and arcing, and which is capable of operating properly at higher pressures and temperatures than presently known molded thermoplastic connectors.
Other objects, and the advantages, of the present invention will be made clear to those skilled in the art by the following description of the presently preferred embodiments thereof